The present invention relates to the general field of gas turbine casings, and more particularly to retention casing for gas turbine fans in aeroengines.
In a gas turbine aeroengine, a fan casing performs several functions. It defines the air inlet passage into the engine, it supports an abradable material facing the tips of the fan blades, it supports an optional soundwave absorber structure for noise treatment at the inlet to the engine, and it incorporates or supports a retention shield. The shield constitutes a trap for retaining debris such as ingested bodies or fragments of damaged blades that are projected outwards by centrifugal force, so as to prevent them from passing through the casing and reaching other portions of the aircraft.
Proposals have already been made to make a fan retention casing out of composite material. By way of example, reference may be made to document EP 1 961 923 that describes fabricating a composite material casing of varying thickness by a method that includes forming fiber reinforcement out of superposed layers of a fiber texture and densifying the fiber reinforcement with a matrix. According to that invention, the fiber texture is made by three-dimensional weaving with thickness that varies, and it is wound as a plurality of superposed layers on a former of profile that corresponds to the profile of the casing to be fabricated. The fiber preform as obtained in that way is held on the former and it is impregnated with resin prior to polymerizing the resin. Winding a woven texture of varying thickness onto a former, as described in that document, makes it possible to obtain directly a tubular preform that has the desired profile with varying thickness.
In practice, implementing that method raises the problem of holding the fiber preform while it is being wound on the former. During winding, it is appropriate to exert sufficient traction force on each layer of the fiber texture to ensure that the layers are compacted effectively. In particular, that requires the first fiber texture layer that is wound on the former to be secured correctly thereto prior to winding the following layers.